This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The Crane group (Cornell) combines photochemistry and X-ray crystallography to study circadian clock proteins and the enzymatic machinery responsible for the generation of reactive nitrogen species. Both of these systems, which have important physiological roles and biomedical implications, involve structure-function studies of heme-containing proteins [134]. Crystallographic data collected at the iron absorption edge will undoubtedly provide enhanced knowledge of how these proteins function in biological information transfer.